Screening blood tests give an indication of the risk of your baby having fetal abnormalities, such as spina bifida or Down’s syndrome.

The tests check the levels of certain 'risk markers' in your blood.

Risk markers

The three most commonly tested markers are:

1. AFP – Alphafetoprotein, a protein substance produced by your baby.
2. hCG – human chorionic gonadotrophin. You may recognise this as the hormone which your pregnancy test detected. 
3. Oestriols – A type of oestrogen hormone produced by your baby and the placenta.

If you haven't had a nuchal translucency scan, then a screening blood test is carried out between 15 and 20 weeks of pregnancy. Most hospitals test for two or three markers; this is why the tests are called the Double or Triple Test. Some hospitals will test for four markers. The more markers, the more accurate the test:

1. Double Test: tests for AFP and hCG
2. Triple Test: tests for AFP, hCG, unconjugated oestriols 
3. Triple Plus: tests for AFP, hCG, oestriols and other markers.

Many factors can affect the results:

1. Your weight (it’s less accurate if you’re very overweight or underweight). 
2. Race (African-Caribbean women have higher levels of AFP and hCG than Caucasian women). 
3. Carrying twins or more. 
4. Insulin-dependent diabetes. 
5. Recent vaginal bleeding. 
6. Uncertainty about dates. 

Age is also taken into account when calculating a woman’s risk of having a baby with Down’s syndrome, as the risk increases with age.

What to do when you get the results

Remember - these tests cannot tell you if your baby definitely does or doesn’t have a problem. They simply tell you whether there is a high or low chance of a problem.

About 1 in 20 mothers having these tests is given a result that the baby is ‘at higher risk’. Most of them will go on to have healthy babies free from problems. But a ‘low risk’ result means the chances of problems are very small.

1. If you are given a ‘high risk’ result: you could do nothing or go on to have further tests.
2. If you are given a ‘low risk’ result: you could do nothing or have further tests, although these are unlikely to be offered by the hospital.